manning said:
I think we are saying the same thing. My reference is that the lens are for the digital camera and thus the conversion factor,1.6, doesn't apply IE 18mm will be 18mm not 28mm. I didn't mean the ef-s could be used on a film camera.
I get what you're saying. But I disagree with it.
A 50mm lens on a full-frame film camera has an angle of view of 46 degrees. Put that same lens on a digital camera with a 1.6 focal length multiplier and it has a field of view of 29 degrees.
A 50mm EF-S lens on a full-frame film camera would have a field of view of 46 degrees (except of course it wouldn't talk to the camera properly) Put that same lens on a digital camera with a 1.6 multiplier and it has a field of view of 29 degrees.
When you talk about a "50mm" lens, the 50mm refers to the lenses focal length, which is the distance between the lens and its focal point, i.e. the film or sensor.
Since digital camera sensors are generally smaller than a frame of 35mm film, the sensor see less than the film does at any given focal length. What the sensor sees at a focal length of 50mm is equivelent to what film sees at a focal length of 80mm - hence the 1.6 multiplier.
But a 50mm Canon EF-S lens has a focal length of 50mm, just like a 50mm EF lens. Focal length is focal length; both lenses will give you the same field of view when put onto a Canon Digital Rebel or D20. The 1.6 multiplier still applies.
I verified this the day I got my Digital Rebel by putting the EF-S 18-55mm lens on it, setting it to 50mm, and taking a shot. Then I put my Sigma 28-80 lens on it, set it to 50mm, and took a shot. Both shots covered the sameframe, even though one is an EF-S lens and the other was made before Canon ever even had a line of digital SLRs.
See here:
http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_Multiplier_01.htm
and here:
http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm
for more complete explanations.